i-adjectives end in い and only い, they never end in き、し、ち、ひ、etc. And it doesn't have to include a kanji in its spelling to be an i-adjective, e.g. すごい is usually written in kana but is an i-adjective. Of course, すごい also has a kanji variation, 凄い, but so does きれい, 奇麗. Whether kanji are usually included in the spelling doesn't change anything. The only way you can distinguish them is:
if adjective ends in anything but い
then it's a na-adjective
else it may be either of them (most of the time it's an i-adjective）
i-adjectives end in い and
i-adjectives end in い and only い, they never end in き、し、ち、ひ、etc. And it doesn't have to include a kanji in its spelling to be an i-adjective, e.g. すごい is usually written in kana but is an i-adjective. Of course, すごい also has a kanji variation, 凄い, but so does きれい, 奇麗. Whether kanji are usually included in the spelling doesn't change anything. The only way you can distinguish them is:
if adjective ends in anything but い
then it's a na-adjective
else it may be either of them (most of the time it's an i-adjective）